The present invention relates to ink-jet printing apparatus and particularly to an ink-jet printing apparatus adapted to project ink droplets from a plurality of nozzles onto a recording medium and thereby to print or record a picture or characters thereon in accordance with an information signal.
There have been proposed and practically used various types of ink-jet printing apparatus for recording information on a recording medium by ejecting ink droplets from a nozzle to which ink is supplied from an ink reservoir.
One type of such apparatus has an electromechanical transducer (hereinafter referred to simply as electrostrictive element) mounted on the nozzle to which ink is supplied, this electrostrictive element being supplied with a high-frequency voltage so as to vibrate the nozzle. The nozzle projects from its tip end ink drops responsive to the period of the vibration and the ejected ink drops are charged in synchronism with the injection timing thereof. The charged ink drops are deflected in accordance with the amount of charge thereon to form a record pattern on a recording medium (this is commonly called the charge modulation system).
Another type of the apparatus is arranged such that, for example as disclosed in U.S. Pat. No. 3,946,398 entitled "Method and Apparatus for Recording with Writing Fluids and Drop Projection Means therefor", the recording apparatus comprises an ink chamber, or a pressure chamber to which ink is supplied from an ink reservoir, an electrostrictive element, or pressure plate provided on the pressure chamber, and a nozzle head, or a printing head having an orifice which communicates with the pressure chamber so as to eject ink drops therefrom, and that the electrostrictive element, or pressure plate, when supplied with an information signal, changes the volume of the ink chamber, or pressure chamber and displaces the ink responsive to the information signal, thereby causing ink droplets to project from the orifice at the rate of one drop for each pulse of the information signal and to form a desired record pattern on a recording medium (this is called the pulse-jet system).
In these conventional types of the apparatus, the former type in which ink drops are projected from a nozzle in synchronism with the period of nozzle excitation charges each of the ink drops used for recording in accordance with the information signal at the time of separation of the ink drop from the nozzle. Therefore, this apparatus can print or record at a high speed, but requires measures for preventing the ink from changing its physical characteristics and an additional device for collecting unrequired ink drops which have not been used for recording.
On the other hand, in the latter type, each information pulse signal is supplied only when an ink drop recording is required and the nozzle orifice projects the ink drops at the rate of one drop for each information pulse signal. Therefore, its recording speed is lower than that of the charge modulation system but this type of system is advantageous in that its nozzle head is simplified in construction and it does not require any measures for collecting unnecessary ink drops and for deflecting the ink drops, with the result that the whole apparatus is made small in size. This type of system is attractive as a simple ink-jet printing apparatus.
In a practical apparatus of this pulse-jet system, a plurality of ink chambers are generally provided in parallel in a single nozzle head and driven individually. Thus, electric pulses of information are amplified by amplifying means which are connected to the respective electrostrictive elements provided correspondingly to the ink chambers, respectively, and then applied to the electrostrictive elements.
Specifically, as disclosed in Japanese patent application laid-open no. 55237/76, a given number of amplifiers each comprising resistors, capacitors and transistors are connected to the electrostrictive elements which are provided at the respective ink chambers formed by pressure chambers, and supply outputs to drive the corresponding electrostrictive elements. In addition, another method is known in which the outputs from a pulse generator are amplified by amplifiers the number of which corresponds to that of the ink chambers and then supplied to the primary sides of pulse transformers whose secondary sides are connected to the respective ink chambers.
Thus, in such conventional types of apparatus, the pulse signal voltages used to drive the electrostrictive elements provided at the respective ink chambers are as high as 250 to 300 volts with pulse width of about 50 .mu.s and therefore amplifiers and pulse transformers are necessary in order to obtain drive voltages for the electrostrictive elements.
Further, the components used in the driving circuits for the electrostrictive elements are required to have a high breakdown voltage and the driving circuits are large-sized and complicated. In addition, the outputs of the amplifiers used must be adjusted to be constant and thus much labor is required.
Then the present inventors have studied another charge modulation system having a plurality of nozzles in which the output of an information signal source and the output of a signal distributor driven by a clock signal are used to deliver output signals from amplifiers in a time sharing mode to the respective nozzles which are connected to the amplifiers, so that the circuit arrangement can be simplified.
This circuit arrangement, however, has disadvantages in that it requires a special signal distributor for distributing the outputs of the amplifiers to the nozzles and it is also unable to drive the nozzles simultaneously or drive each of the nozzles at any desired time, because the nozzles must be operated in a predetermined order.